The disclosures of Japanese Patent Applications Nos. 2000-196120 and 2001-40685 filed on Jun. 29, 2000 and Feb. 16, 2001, respectively, including the specifications, drawings and abstracts, are incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to engine valve drive control apparatus and method for controlling driving of engine valves of an internal combustion engine based on electromagnetic force generated by electromagnets.
2. Description of Related Art
Valve drive apparatuses for driving engine valves, such as intake valves and exhaust valves, of internal combustion engines, by controlling electromagnetic force of electromagnets have been known. The valve drive apparatus of this type is desired to ensure high operating stability when driving the engine valves. Furthermore, it is desirable to minimize the amount of electric power that is consumed for driving the engine valves, and to suppress occurrence of noises upon opening and closing of each engine valve by reducing its drive velocity when the engine valve reaches either one of the opposite ends of its stroke (or a range of its displacement), namely, the fully closed position or the fully open position.
In a conventional apparatus as disclosed in Japanese Patent laid-open Publication No. 9-217859, the actual operating state of the engine valve is detected, and the electromagnetic force generated by an appropriate electromagnet is controlled so that the actual operating state coincides with a target operating state of the valve. In this manner, the electromagnetic force of the electromagnet is controlled to a magnitude that meets various requirements as mentioned above.
When controlling the electromagnetic force generated by the electromagnet, the apparatus as disclosed in the above-identified publication operates to determine a positional deviation between the actual position of an engine valve and a target position thereof (e.g., a fully open position or a fully closed position), and apply a controlled current to the electromagnet so that the resulting electromagnetic force has a magnitude suitable for displacing or moving the engine valve to the target position. If the positional deviation is large, for example, the exciting current applied to the electromagnet is increased so that the engine valve is opened or closed with accordingly increased electromagnetic force.
It should be noted, however, that the engine valves are subjected to external forces that vary depending upon the engine load. The external forces exerted on each engine valve are produced by, for example, the internal pressure (or in-cylinder pressure) within a corresponding combustion chamber, and the intake pressure or the exhaust pressure. Therefore, if the electromagnetic force of the electromagnet(s) is controlled based solely on information on the position of the engine valve in question (e.g., a positional deviation), the electromagnetic force may become insufficient when the drive force required to drive the engine valve is increased due to the influence of the external forces. In this case, the engine valve may not exhibit sufficiently high operating stability. If the electromagnetic force is set in advance to be sufficiently large so as to avoid the above situation, on the other hand, the engine valve may be driven by an excessively large electromagnetic force, depending on the condition of the engine load. This may result in increased power consumption, and occurrence of noise and vibrations at the time of opening and closing of the engine valve. In order to appropriately control the electromagnetic force for driving the engine valve, therefore, it is necessary to control electric current applied to the selected electromagnet in accordance with the engine load so that the influence of the external forces is taken into consideration.
To control current applied to the electromagnet in accordance with the engine load, it is necessary to obtain the relationship between the engine load and the electromagnetic force suitable for the engine load through experiments or the like, in addition to the information in the position of the engine valve, and to pre-set the relationship in the form of a control map, for example. Thus, it takes a great amount of time to perform operations to correlate control constants or parameters.
It is therefore an object of the invention to provide an engine valve drive control apparatus and method which enable an engine valve to be driven with an appropriate electromagnetic force that is controlled in accordance with the engine load, and which permits a significantly simplified operation to correlate control constants used for control of driving of the engine valve.
To accomplish the above and/or other object(s), one aspect of the invention provides a drive control apparatus for controlling driving of an engine valve of an internal combustion engine based on an electromagnetic force generated by at least one electromagnet. The apparatus includes a controller that sets a target drive velocity of the engine valve in accordance with a displacement of the engine valve, such that the target drive velocity corresponds to a velocity of the engine valve when there is no engine load. The controller then controls a magnitude of the electromagnetic force by controlling current applied to the electromagnet, depending upon a degree of separation between an actual drive velocity of the engine valve and the target drive velocity, so that the actual drive velocity is made substantially equal to the target drive velocity set by the setting unit.
When the drive force required to stably or reliably drive the engine valve changes in accordance with the external force that depends upon the engine load, the actual drive velocity deviates or separates from the target drive velocity that corresponds to the velocity of the engine valve in a no-engine-load state, because of the influence of the external force.
With the drive control apparatus constructed as described above, if the actual drive velocity deviates from the target drive velocity (in a no-engine-load state) due to the influence of the engine load, electric current applied to an appropriate electromagnet is controlled depending upon the degree of separation between the actual and target drive velocities. In this manner, the electromagnetic force of the electromagnet is controlled so that the actual drive velocity substantially coincides with the target drive velocity. Thus, even if the external force acting on the engine valve varies depending upon the engine load, the engine valve is driven with a suitably controlled electromagnetic force that corresponds to the engine load, so as to ensure opening and closing characteristics that are equivalent to those provided when there is no engine load. Furthermore, when controlling the electromagnetic force of the electromagnet depending upon the engine load as described above, there is no need to perform an operation to empirically determine the relationship between the engine load and the electromagnetic force suitable for the engine load, through experiments or the like. Rather, it is simply required to set the target drive velocity in a no-engine-load state in accordance with the displacement (or position) of the engine valve. It is, therefore, possible to greatly simplify an operation to correlate control constants.